Epoxy coating systems cured with polyamine-based curing agents are used for the preparation of industrial maintenance coatings and other types of protective coatings for a variety of substrates. Epoxy resins have excellent resistance to chemicals also have good adhesion to most substrates, e.g. various woods, wall-boards, metals and masonry surface.
There has long been a desire to formulate a curing agent which is essentially free of volatile organic compounds (VOC's), which are self emulsifiable and curable at a wide range of temperatures in the absence of external accelerators if possible.
Many of the current waterborne epoxy resins and curing agents are plagued with the problem of poor film properties because the surfactants tend to migrate to the surface during the cure of the resin system. Thus, it would be desirable to provide a curing agent system containing a surfactant which does not migrate during cure, that is, a self emulsifiable system which does not require salting the surfactant, e.g. with acids, or using plasticizers to stably disperse the curing agent in water.
In addition to providing a self emulsifiable waterborne curing agent, the curing agent should be readily compatible with a waterborne epoxy resin in order to make a coating having good mechanical properties and weatherability. A waterborne curing agent that does not have good compatibility with the epoxy resin will not coalesce well when applied onto a substrate. The problem of compatibility is more acute where the curing agent primary amine groups have been converted to secondary amine groups to reduce the blooming or hazing phenomena.
Due to more stringent environmental regulations particularly with respect to reduced volatile organic compounds (VOC), toxicity, etc. aqueous based coating systems (waterborne epoxy resin systems) are receiving significant attention in terms of research and development efforts.
These curing agents for waterborne epoxy resins are typically water-dilutable polyamines that are either inherently water soluble or whose water solubility is enhanced by means of reaction with an organic acid such as acetic acid. Those that are highly water compatible provide for coatings which exhibit water sensitivity and poor protection from corrosion.
For example, in U.S. Pat. No. 5,489,630 describes a waterborne curing agent based on low molecular weight polyetheramine are water soluble. These low molecular weight polyetheramine have high levels of water-soluble polyethers which may lower the aqueous chemical resistance of paints.
It is desirable to obtain curing agents that are incompatible with water but dispersible in water and further can be water dispersible without the aid of an acid.